1. Field of the Invention
The present invention relates to a projection image display device having a dust-proof structure.
2. Description of the Background Art
Brightness of a projector has been improving year by year. The improved brightness creates a great advantage for a user in terms that a clear image can be seen even in a lighted environment.
Meanwhile, in accordance with the improved brightness, a heat generation amount inside the projector has been increasing. Particularly with optical parts, the more the brightness is improved, the more a heat receiving amount is increased. Thus, a cooling unit is essential for ensuring performance and safety. Conventionally, there are various methods for cooling optical parts. Among the methods, a method of taking external fresh air into a projector casing and blowing the air to the optical parts for cooling has been most frequently adopted, since the method is realizable with an inexpensive and simple structure.
However, taking the external air in means that external dust is taken in at the same time. The dust attached onto the optical parts emerges as a shadow or a bright spot in a projected image, so that quality of the image is remarkably diminished. Therefore, there is a need for removing the dust. As a measure for this, there is a general method of providing an air filter, and also, there is a technology for improving a dust-proof property (for example, refer to Japanese Patent Application Laid-Open No. 10-200837 (1998)).
The air filter itself serves as air resistance when the external air is suctioned. When the air filter is used for a long time, clogging is caused due to the dust, leading to a further decrease in a cooling ability. Therefore, there is a need for regular maintenance such as cleaning and replacement. For example, with the projector installed in a high place, performing any operation is highly troublesome. Thus, dust-proof measures to be used for a long time while avoiding the maintenance as much as possible has also been developed (for example, refer to Japanese Patent Application Laid-Open No. 06-59247 (1994)).
With the conventional inventions, it is difficult to inexpensively realize both simplicity of the maintenance and minimization of the decrease in the cooling ability.
For example, in the technology according to Japanese Patent Application Laid-Open No. 10-200837 (1998), two air filters are integrally formed, and the two air filters are simply provided. Therefore, the air resistance of suction air is increased, and there is room for improvement in terms of the decrease in the cooling ability.
In the technique according to Japanese Patent Application Laid-Open No. 06-59247 (1994), the maintenance is simplified by providing an air filter rotatably. However, in a case where the air filter is moved by using an actuator, there is a plurality of moving directions. Thus, a structure is complicated and becomes expensive as a result. Alternatively, in a case where the air filter is manually moved, an advantage of the simplicity of the maintenance is diminished.